Industry's Fastest Insulation Tester Assesses in as Fast as 50ms
The Hioki electrical safety testers are designed for insulation resistance and voltage withstand testing of electrical devices and components according to various safety standards. The ST5520 is the fastest insulation tester in the industry, delivering pass/fail assessment in as fast as 50 ms. 25 to 1000 V test voltage with 1 V resolution.

Key Features

• Rapidly assess in as fast as 50 ms
• Measure and save data in as fast as 2 seconds, a 60% improvement from the legacy 3554
• Quick discharge of residual voltage
• Freely configurable test voltage (set from 25 V to 1000 V, 1 V resolution)
• Contact check function (prevents errors due to poor contact)
• MShort-circuit check function (stops potential defects from reaching the market)
• Ideal for battery production lines

Model No. : ST5520
Built-in external I/O output

Model No. : ST5520-01
Built-in BCD output

Industry’s Fastest Testing Speed

The Insulation Tester ST5520 delivers the fastest insulation resistance testing in the industry, meeting all the requirements of production lines thanks to rapid takt times.

Rapidly assess in as fast as 50 ms

Testing is complete in as little as 50 ms — the fastest time in the industry. This is 700 ms faster than legacy Hioki models.

Quickly discharge residual voltage

The post-test residual voltage discharge time has been reduced significantly compared with legacy models. As a result, when comparing an identical sample under the following conditions, a takt time improvement of 990 ms is estimated.

Prevents errors due to poor contactbr />

The contact check function allows you to check that proper contact has been made with the device under test prior to the testing. This ensures that resistance testing is not carried out without proper contact, as this can result in erroneous assessment.
There are two methods: 4-wire contact check and comparator contact check.

Stops potential defects from reaching the market

With this function, a low voltage (2 V to 4 V DC) is applied to the test patterns to check for micro-shorting prior to insulation testing.

New leads for more convenient measurement in distribution panels and other confined locations

The Pin Type Lead L2020 with L-shaped tips is available as a new option. The design significantly improves ease of use when inspecting batteries installed in confined locations.

Safe, easy operation at your fingertips

The use of optional Switched Probe 9299 lets you to operate the ST5520 while holding the probe.


Basic specifications (Accuracy guaranteed for 1 year, Post-adjustment accuracy guaranteed for 1 year)

Measurement itemsInsulation resistance (Applied DC voltage method)
Testing voltage(Measurement range: AUTO/MANUAL setting is possible)
25 V ≤ V < 100 V (2.000/20.00/200.0 MΩ),
100 V ≤ V < 500 V (2.000/20.00/200.0/2000 MΩ),
500 V ≤ V ≤ 1000 V (2.000/20.00/200.0/4000 MΩ)
Basic accuracy±2 % rdg. ±5 dgt.
25 V ≤ V < 100 V [0 to 20 MΩ]
100 V ≤ V < 500 V [0 to 20 MΩ]
500 V ≤ V ≤ 1000 V [0 to 20 MΩ]
Measurement speedFast: 30 ms/time, Slow: 500 ms/time (selectable)
DisplayLCD (service life: 100,000 hours), 4-level backlight
Internal memorySaved items: rated measurement voltage, comparator upper limit /lower limit values, test mode, beep sound to distinguish the result, test time, response time, resistance range, measurement speed
Memory capacity: up to 10 items (can be saved/loaded)
Comparator settingUPPER_FAIL: Measured value ≥ upper limit value
PASS: Upper limit value > measured value > lower limit value
LOWER_FAIL: Measured value ≤ lower limit value
Judgement processBeep sound, PASS / U.FAIL/L. FAIL: light up on LED display, When UL_FAIL, U.FAIL / L.FAIL light up simultaneously, EXT.I/O output, judgement result can be obtained via RS-232C
Test durationDefinition of test duration: Test duration = Response time + Measurement time
Function: Set the time from voltage application until pass/fail assessment
Configuration range: 0.045 s to 999.999 s (0.001 s resolution)
Response time timerAfter the start of the test, comparator judgment operation can be prohibited until a set interval from 0.005 sec. to 999.999 sec. (at 0.001 sec. resolution) has passed.
Analog outputDC +4 V f.s.
InterfaceRS-232C (standard), External I/O (External control input, Judgment result)
BCD output (ST5520-01 only)
Power supply100 to 240 V AC, 50/60 Hz, 25 VA max.
Dimensions and mass215 mm (8.46 in)W × 80 mm (3.15 in)H × 166 mm (6.54 in)D, 1.1 kg (38.8 oz)
AccessoriesInstruction Manual ×1, Power cord ×1, EXT. I/O Connector ×1, Connector Cover ×1

Catalog : INSULATION TESTER ST5520Download PDF  English
Catalog: INSULATION / WITHSTANDING Test Instrument series 3153, 3159, 3174, ST5520Download PDF  English
Catalog: Motor Measurement ApplicationsDownload PDF  English


User Guide: Electrical Measurements of Lithium-Ion BatteriesDownload PDF  English
User Guide:
Insulation Tester ST5520/ST5520-01 Programming Command Compatibility with 3154
Download PDF  English